1. Field of the Invention
This invention generally relates to electrical cord clamps for use on electrical plugs and connectors.
2. Description of Related Art
An electrical cord may be terminated in an electrical plug or cap having male-type prongs, or in an electrical connector having female-type sockets. In use, the cord may be subjected to external forces tending to pull the cord from the plug or connector. To resist such pulling forces, automatic cord clamping devices have been proposed for circumferentially clamping the cord.
In one known prior art construction, the clamping device consists of a shell into which a main body is inserted. The shell has a hole of a predetermined diameter into which the cord is inserted along a longitudinal direction or axis. The main body carries at least one electrical terminal to which the cord is connected. In the case where the cord includes hot, neutral and ground wires, three corresponding screw terminals are provided on the main body.
To achieve the clamping function, a set of movable arms extends inwardly from the main body and is arranged along an annulus whose diameter is several times greater than said predetermined diameter. A set of cams is provided within the shell. During insertion of the main body into the shell, the cams push the arms through a comparatively large distance toward said axis, thereby circumferentially clamping the cord.
However, experience has shown that the known clamping devices are not altogether satisfactory in reliably resisting forces which tend to pull the cord from the device. The known movable arms which are integrally molded with the main body have to be manually inwardly displaced toward the axis prior to inserting the body into the shell in order to reliably assemble the body inside the shell without mechanical interference therewith. This represents an extra time-consuming step in the wiring installation.
Also, the known movable arms each have to be moved through a comparatively large distance, e.g. about 1/2, to clamp the cord. To traverse this comparatively large distance and to enable an installer to inwardly displace the arms prior to insertion, each arm has to be readily flexible. However, by imparting a high degree of flexibility to the arms, there is no inherent tendency by the arms themselves to lock against the cord. The arms, therefore, according to the known prior art constructions, act on the cord in a non-locking manner. Hence, the known prior art clamping devices do not reliably resist cord pulls, since pulling on the cord generates a force which actually tends to open up the relatively flexible arms.